1. Field
The present invention relates generally to communication, and more specifically to techniques for detecting signaling bits such as paging indicator bits.
2. Background
A wireless device (e.g., a cellular phone) in a wireless communication system is typically designed to operate in one of several modes, such as an “active” mode or an “idle” mode, at any given moment. In the active mode, the wireless device can actively exchange data with one or more base stations in the system, e.g., for a voice or data call. In the idle mode, the wireless device typically monitors a paging channel (PCH) for messages applicable to the wireless device. Such messages may include page messages that alert the wireless device to the presence of an incoming call and overhead messages that carry system and other information for the wireless device.
In the idle mode, the wireless device continues to consume power in order to monitor the signals transmitted by the base stations in the system. The wireless device may be portable and powered by an internal battery. Power consumption by the wireless device in the idle mode decreases the available battery power, which then shortens both the standby time between battery recharges and the talk time when a call is placed or received. Therefore, it is highly desirable to minimize power consumption in the idle mode in order to increase battery life and extend standby time.
In one common technique for reducing power consumption in the idle mode, user-specific messages are sent on the paging channel to the wireless device at designated times, if at all. The paging channel is divided into numbered PCH slots. The wireless device is assigned specific PCH slots on which it may receive user-specific messages. With such a slotted paging channel, the wireless device can operate in a “slotted” mode whereby it periodically, rather than continuously, monitors the paging channel for messages from the base stations in the system. In the slotted mode, the wireless device wakes up from a “sleep” state prior to its assigned PCH slot, enters an “awake” state, and processes the paging channel for messages. The wireless device remains in the awake state if a received message requires the device to perform additional tasks, and reverts back to the sleep state otherwise. In the time period between successive presences in the awake state, the wireless device is in the sleep state and the base stations do not send any pages or user-specific messages to the wireless device. The wireless device powers down as much circuitry as possible in the sleep state in order to conserve battery power.
In another technique for further reducing power consumption in the idle mode, a quick paging channel (QPCH) is used to indicate whether a page message might be transmitted on the paging channel for the wireless device. For cdma2000, the quick paging channel carries a number of paging indicator bits that are transmitted as binary On/Off bits. The wireless device is assigned two paging indicator bits for each QPCH slot associated with an assigned PCH slot. The wireless device is able to quickly detect the paging indicator bits and to immediately enter the sleep state without processing the paging channel if the paging indicator bits indicate that no message will be transmitted on the paging channel for the wireless device.
Accurate detection of the paging indicator bits is important to achieve good performance and improve standby time. Erroneous detection of the paging indicator bits as On when they are actually Off leads to an increase in the awake time to process the paging channel for messages that are not sent. Conversely, erroneous detection of the paging indicator bits as Off when they are actually On may lead to missed page messages, which may result in missed calls. All of these effects are undesirable.
There is therefore a need in the art for techniques to accurately detect paging indicator bits.